The cochlea has what type of organization?
The Organ of Corti is located in which part of the cochlea?
Scala Media (Cochlear duct)
What type of sensory innervation does the Scala media have?
Special somatic afferent innervation
Inner hair cells have what type of innervation?
Primarily afferent innervation but some efferent to the Spiral ganglion.
Outer hair cells have what type of innervation?
Primarily efferent innervation with some afferent, controlling the tectorial membrane.
In the ascending auditory system, the only part of this pathway that is unilateral and that’s not binaural?
After you get past the cochlear nucleus, what changes in the auditory pathway?
Things become bilateral
If you damage the cochlear nucleus, what can happen?
unilateral, sensorineural deafness
If you damage anything past the cochlear nucleus, what can happen?
There is so much crossover, you will still have bilateral hearing
What are the two major parts the cochlear nucleus is broken up into?
- Anterior cochlear nucleus (ACN)
- Posterior cochlear nucleus (PCN)
What is the anterior cochlear nucleus (ACN) broken up into? (2)
- Ventral posterior cochlear nucleus
- Ventral anterior cochlear nucleus
What is special about the anterior portion of the anterior cochlear nucleus (ACN)?
It is tonotopically oriented
The spiral ganglion is located where and what type of neurons are they associated with?
- Located in the cochlea
- Location of first-order neurons
Bipolar neurons run from what types of cells to the spiral ganglion? Where do they go after?
Bipolar neurons that run from inner hairs and outer hair cells to spiral ganglion. After the spiral ganglion, they run to the cochlear nucleus
What are the 3 areas of the cochlear nucleus that the spiral ganglion project to?
- anterior cochlear nucleus (AVCN - anterior ventral cochlear nucleus)
- dorsal (posterior) cochlear nucleus (DCN)
- posterior (portion of the) anterior cochlear nucleus (VPCN - ventral posterior cochlear nucleus)
What cell types make up the Dorsal Cochlear Nucleus (DCN)? (2)
- Pyramidal cells
- stellate cells
The Dorsal Cochlear Nucleus (DCN) send projections via what?
They send afferent projections to the higher portions of the brainstem (pons) via the Dorsal Acoustic Stria (DAS)
The Ventral Posterior Cochlear Nucleus (VPCN) send projections up to the upper portion of the pons via what?
Intermediate Acoustic Stria (IAS)
What cell types make up the Anterior Ventral Cochlear Nucleus (AVCN)? (2)
- Stellate cells
- Bushy cells
What is the primary projecting pathway in the auditory pathway that projects to the third order neurons?
Ventral acoustic stria (trapezoid body) from the Anterior Ventral Cochlear Nucleus (AVCN)
How does the Anterior Ventral Cochlear Nucleus (AVCN) project to third-order neurons?
Ventral Acoustic Stria aka Trapezoid Body
What is the first nucleus that is projected to from the cochlear nucleus?
Superior olivary nucleus
What does the Superior olivary nucleus project up to?
- Nucleus lateral lemniscus
- Inferior colliculus
What does the Ventral Acoustic Striae (Trapezoid Body) project to in the midbrain?
The dorsal acoustic striae (DAS) will bypass what and also go to the inferior colliculus?
The lateral lemniscus nucleus
What is a housing point (nuclei) for neurons in the midbrain?
Nucleus lateral lemniscus
What is the tract of ascending neurons that synapse at the inferior colliculus of the midbrain?
If a tract does not synpase in nucleus lateral lemniscus before ascending to the inferior colliculus, what do you not have?
It does not become a fourth-order neuron. It stays whatever type of neuron it was prior to projecting out.
Where are first-order neurons in the auditory tract?
At the spiral ganglion in the cochlea
Where are second-order neurons in the auditory tract?
Cochlear nucleus in the medulla
Where are third-order neurons in the auditory tract?
Superior olivary nucleus in the pons
Where are fourth-order neurons in the auditory tract?
Nucleus lateral lemniscus in the midbrain
Where are fifth-order neurons in the auditory tract?
Inferior colliculus in the midbrain
What is special about the Brachium of the Inferior Colliculus?
It maintains the tonotopic orientation in the AVCN that is relayed by trapezoid body until it reaches the fifth-order neuron, inferior colliculus.
Where does the tonotopic information go from the inferior colliculus?
inferior colliculus –> medial geniculate nucleus (MGN)–> auditory cortex (transverse temporal gyri) also known as Heschl’s gyri.
What is auditory agnosia?
You can hear sound, can tell you they heard the sound, but have no idea what that sound was.
What is Wernicke’s aphasia? What Brodmann’s area is it?
They can hear speech, but have no idea what you are saying
Brodmann’s area 22
What is Broca’s aphasia? What Brodmann’s area is it?
The brain can still transmit information via the arcuate fasciculus to Wernicke’s area.
They can understand sound, but cannot formulate sounds and words to communicate back to you
Brodmann’s area 44, 45
Transverse gyrus of Heschel is interchangeable with what term? Where is this located?
Superior Transverse Gyrus (STG) found in the primary auditory cortex
More interior in the auditory cortex is _____ and more exterior is more _____.
- High frequencies
- Low frequencies
If neuron signaling in the auditory pathway want to get to the inferior colliculus from the cochlear nucleus or above, what pathway must they use?
What are the two portions of the superior olivary nucleus and what do they do?
- Medial superior olivary nucleus (Localization based on Timing [if the right side is being stimulated before the left side])
- Lateral superior olivary nucleus (Localization based on Intensity [loudness of sound, aka coincidence detection])
What does a special task that the trapezoid body does to one of the portions of the Superior Olivary Nucleus?
The trapezoid body of the activated ear (R) sends inhibitory neurons to the (R) Lateral superior olivary nucleus telling the brain that we are hearing out of the (R) ear. It works by slowing down the relay of information to that nucleus in the ascending pathway.
R ear –> L primary auditory cortex
What is the projection called from the Superior Olivary Nucleus to the cochlea?
Olivocochlear bundle (OCB) from the Medulla
What does the Olivocochlear Bundle projection from the Superior Olivary Nucleus do?
It can dampen sounds, via a reflex pathway, that changes the organization of the outer hair cells and elongates them. It pushes the tectorial membrane away [when elongated] from the inner hair cells and protects them and lessens the ability to hear sounds.
Following a CVA, a 73-year-old male is unable to formulate speech without evidence of dysarthria. Which area is most likely involved?
How do you remember the order of how information travels in the auditory pathway?
E - eighth nerve
C - cochlear nucleus
O - superior olivary nucleus
L - lateral lemniscus
I - inferior colliculus
The middle ear has two muscles, what is on the anterior wall and the posterior wall? What are their innervations?
Anterior wall: tensor tympani muscle, trigeminal n.
Posterior wall: stapedius muscle, seventh n. (facial)
Innervation = first letter of their name
The brain stem uses innervation to protect the ear itself from loud noises called the stapedius reflex. Describe this reflex.
Sound relays to the Superior Olivary nucleus and the facial nucleus is right next to it. The facial nerve innervates the stapedius muscle (Seventh cranial nerve).
An involuntary muscle contraction (stapedius m.) occurs in the middle ear in response to high-intensity sound stimuli or when the person starts to vocalize.
Brodmann’s area 41, 42, and 22 are associated with what reflex?
Acoustic startle reflex (Postural reflex). When there is a loud noise, you will turn in that direction.
What contains axons from only 2nd, 3rd, and 4th order neurons in the acoustic pathway?
Nucleus lateral lemniscus
What is the connection between the cochlear nucleus and the superior olivary nucleus?
Ventral acoustic striae (Trapezoid body)
The only way to get to the inferior colliculus is via what?
Where is the only point in the auditory pathway where you will have unilateral hearing loss? Why?
The cochlear nucleus because after that there is crossing over.
How do you get from the inferior colliculus to the medial geniculate body?
Brachium of the inferior colliculus (BIC)
Conductive hearing loss in terms of Rinne and Weber?
Rinne: Abnormal (bone > air)
Weber: Localizes to affected ear
Sensorineural hearing loss in terms of Rinne and Weber?
Rinne: Normal (air > bone)
Weber: Localizes to unaffected ear